In magnetooptical recording, information in the form of magnetic domains is written on a magnetooptical recording layer having perpendicular magnetic anisotropy. This information is read by irradiating the medium with a linearly polarized laser beam and detecting the change of the incident laser beam caused by the interaction of the light with the magnetization. Kerr rotation, coercivity, sensitivity and carrier to noise ratio (CNR) are critical parameters to be concerned with to achieve high performance magnetooptical recording. The Kerr rotation angle is the amount of rotation of polarized light from incident linearly polarized light when it is reflected from the magnetic media, while the sensitivity of the medium depends upon its coercivity and Curie temperature.
Magnetooptical recording is desirable because it is capable of high density information storage, while also having the capability of being erasable. Currently, rare-earth, transition-metal alloy films are favored as the recording media in magnetooptical recording elements. A useful medium of this type is disclosed in U.S. Pat. No. 4,670,353 issued June 2, 1987 and comprises a TbFeCo alloy.
An inherent disadvantage of such films is that they are highly susceptible to corrosion and oxidation. For example, aging in low humidity, high temperature environments results in uniform oxidation of the film. On the other hand, in high humidity environments, corrosion pits or pinholes are formed which grow in size and number and in time completely destroy the film.
The problem facing the artisan at the time of this invention has been to provide a magnetooptical recording film having improved corrosion and oxidation resistance without significantly adversely affecting the Kerr rotation, CNR, or sensitivity of the recording element.